The disposal of waste products, such as human and animal digestive waste products, as well as the waste from industries, has always been a major social and economic problem. Such waste products include human and animal digestive waste products, and in addition, liquid waste products from industries, such as pulp and paper, meat slaughtering and packaging, cotton processing, canning, dairy products, sugar refining, frozen foods and vegetables, poultry, hides, leather and wool scouring and the like. Such industries produce waste products characterized by high biochemical oxygen demand levels and a large amount of suspended solids and pathogens. A variety of processes have been employed to render all of these pathogenic waste materials harmless, and to remove them as pollution factors. A great many of these processes employ a system of bacteriological decomposition.
Bacteriological decomposition processes often require enormous storage facilities because of the time required for bacteriological action, such as thirty to sixty days. In a typical process for the treatment of raw sewage, incoming raw sewage containing pathogenic microorganisms is sent through a comminutor where large solid material in the raw sewage is reduced in size, and then the sewage pumped to an aerated grit chamber where grit is removed. Such raw sewage contains less than 1% by weight of solids; for example, less than 2,000 parts per million of solid material. After removal of the grit, the sewage is directed to large settling tanks where the material is held for a period of time to permit settlement of the solids. Oleophilic material, such as grease, is then decantered from the surface of the liquid in the settling tanks, and the supernatant liquid removed from this primary settling tank and sent to a final aeration settling tank for a secondary treatment, and then further, forwarded to a chlorine-contact tank wherein typically about 99.8%, but less than all, of the pathogenic bacteria or microorganisms are killed by chlorine contact. The resulting liquid is then discharged into waterways or further chlorinated and recycled for reuse.
Typically, the raw sewage sludge removed from the primary treatment tank comprises from about 3 to 10% solids, which sludge is removed and sent to a digestion tank wherein the solids are decomposed by the reaction with a seeded bacteria which decomposes the carbohydrate waste material, generating heat and methane gas. The methane gas generated from such digestion tank(s) is often removed and used as fuel for heating the digestion tanks for other fuel purposes. Water is removed from the digestion tank from the decomposed solids, and, thereafter, the aerated or bacteria-digested raw sludge material is then formed into a cake-like material, either by the use of sludge beds or filters to form a moist cake product. The cake product, rich in nitrogen, may then be used for landfill, fertilizer, soil conditioner, or otherwise used or disposed of. Such a treatment process is commonly employed throughout the country to dispose of sewage products.
The decomposed solids or sewage sludge leaving the digestion tank and the supernatant liquid leaving the chlorine-contact tank often fall far short of being pathologically pure, or meeting the minimum standards required for effective pollution control. Numerous chemical methods are available for the further sterilization of these organic waste materials; however, cost and residual toxicity have rendered many of such techniques economically inadvisable.
There are a number of processes for the preparation of nitrogenous fertilizer compositions employing urea-formaldehyde condensates, such as, for example, those techniques described in U.S. Pat. Nos. 2,592,809; 2,644,806; 2,766,283; 2,830,036; 3,076,700; and 3,227,543. In addition, U.S. Pat. Nos. 3,073,693 and 3,226,318 are directed to the employment of polymerizable monomers with sewage solids to produce a synthetic nitrogen-containing fertilizer by-product.
For example, U.S. Pat. No. 3,073,693 prepares a nitrogenous fertilizer material by reacting sewage sludge, peat moss and a urea-formaldehyde solution, and immediately thereafter, condensing the urea-formaldehyde with the use of a strong acid to form a resin product. The reactants are admixed for between 1/2 and 2 minutes in an acid solution, whereby polymerization and condensation of the urea-formaldehyde is effected and the resulting mixture then admixed with an aqueous solution of ammonia to form the ammonium salt of the strong mineral acid. The sewage sludge employed is the type of sludge produced by the activation or digestant method; that is, an activated sterile sewage sludge, which has been removed from the digestion tank and dewatered.
U.S. Pat. No. 3,226,318 is directed to the consolidation by condensation of an aqueous waste sludge wherein a henol-formaldehyde solution is added to the sludge, and promptly thereafter, condensation is accomplished by the further addition of formaldehyde as a curing agent. This sewage treatment process is directed to a sewage sludge containing digested sewage solids and about 60% water in which a phenol-formaldehyde solution under acid conditions is condensed to provide a consolidated sludge product.